The present invention relates to an improved process for the production of thiocarbohydrazide.
Several processes for the manufacture of thiocarbohydrazide (TCH) are known. TCH may be obtained during the hydrazinolysis of thiophosgene in moderate yields using ether or water as the reaction medium. It is also known to manufacture TCH by hydrazinolysis of diethylxanthate (Guha et al., J. Chem. Soc. 125, 1215 (1924)). Simply heating the two reaction components in the absence of a solvent results in yields of 70-74% of theory. (Beyer et al., Ber. 87, 1401 (1954)).
It is also known to prepare thiocarbohydrazide through conversion of dialkyltrithiocarbonates with hydrazine. Cyclic trithiocarbonate may also be used for this synthesis. Ethylenetrithiocarbonate, for example, generally gives pure thiocarbohydrazide in a yield of about 71% of theory. The hydrazinolysis of methyldithiocarbazinate typically leads to a yield of 65% of theory of thiocarbohydrazide.
The most common synthesis of thiocarbohydrazide is, however, the conversion of carbon disulfide with hydrazine. Hydrazinium-dithiocarbazinate (HDTC) forms according to equation (1): EQU CS.sub.2 +2H.sub.2 NNH.sub.2 .fwdarw.H.sub.2 NNHCSSH.NH.sub.2 NH.sub.2( 1)
This compound is then converted to thiocarbohydrazide with evolution of hydrogen sulfide according to equation (2): EQU H.sub.2 NNHCSSH NH.sub.2 NH.sub.2 .fwdarw.H.sub.2 NNHCSNHNH.sub.2 +H.sub.2 S(2).
Better yields and pure product are obtained when the hot aqueous solution of the hydrazinium-dithiocarbazinate is digested with lead oxide (Stolle, et al., Ber. 41, 1099 (1908)).
The yields of thiocarbohydrazide can also be increased when conducting the decomposition of hydrazinium-dithiocarbazinate in aqueous solution in the presence of hydrazine (U.S. Pat. No. 2,726,263). It has been found that increasing the amount of water in the hydrazine-containing reaction medium decreases the yield of TCH. The use of a waterfree solvent for hydrazine (e.g., methyl, ethyl, or propyl alcohol), however, does not increase the TCH yield. In the process disclosed in U.S. Pat. No. 2,726,263, the hydrazinium-dithiocarbazinate (obtained in the usual way through conversion of carbon disulfide with hydrazine hydrate), is heated in an aqueous hydrazine solution at approximately 95.degree. C. for 1-2 hours under reflux. For each mole of hydrazinium-dithiocarbazinate, 1 to 3 moles of hydrazine are used. In a variation of this known process, carbon disulfide in aqueous solution with 3 to 6 times the amount of hydrazine is cooled and then heated. In both processes, the yield can be increased by repeatedly removing the TCH which forms during the course of the conversion from the reaction mixture. However, the yield is only 53.3% of theory.
It is also known to convert the hydrazinium-dithiocarbazinate thermally. Yields of approximately 70% of theory may be obtained (Petri, Z. Naturforsch, 16B, 769 (1961)) by such thermal decomposition.
In each of the above-described processes, any excess hydrazine must be recovered. Such recovery is costly, time consuming and troublesome due to the reactivity and instability of hydrazine.
U.S. Pat. No. 4,294,985 teaches that the mother liquor containing the excess hydrazine may be recycled instead of being recovered. However, recycling of the hydrazine-containing liquor creates new problems. More specifically, recycling results in the build up of impurities which can reduce the yield of TCH. Further, some of the hydrazine containing liquor must be purged from the system after each recycle resulting in loss of hydrazine.
It would therefore be advantageous to deVelop a process for producing TCH which did not require removal or recycling of excess of hydrazine but did produce TCH in high yield.